U.S. patent number 9,778,355 [Application Number 14/613,370] was granted by the patent office on 2017-10-03 for signal processing method and device for frequency-modulated continuous waveform radar system.
This patent grant is currently assigned to Wistron NeWeb Corporation. The grantee listed for this patent is Wistron NeWeb Corporation. Invention is credited to Cheng-Hsiung Hsu, Chi-Cheng Kuo, Jeng-Da Li, Chi-Yung Liao, Chien-Chung Tseng.
United States Patent |
9,778,355 |
Li , et al. |
October 3, 2017 |
Signal processing method and device for frequency-modulated
continuous waveform radar system
Abstract
A signal processing method for a frequency-modulated continuous
waveform (FMCW) radar system includes receiving a plurality of
feedback signals from a plurality of targets and performing analog
to digital conversion on the plurality of feedback signals to
obtain a digital receiving signal corresponding to the plurality of
feedback signals, performing a window function on the digital
receiving signal to obtain a window transformation signal
corresponding to the digital receiving signal, performing
time-domain to frequency-domain conversion on the window
transformation signal to obtain a spectrum signal of the window
transformation signal, performing two beat frequency detections on
the spectrum signal, and determining distances and speeds of the
plurality of targets in comparison to the FMCW radar system
according to results of the two beat frequency detections.
Inventors: |
Li; Jeng-Da (Hsinchu,
TW), Kuo; Chi-Cheng (Hsinchu, TW), Hsu;
Cheng-Hsiung (Hsinchu, TW), Liao; Chi-Yung
(Hsinchu, TW), Tseng; Chien-Chung (Hsinchu,
TW) |
Applicant: |
Name |
City |
State |
Country |
Type |
Wistron NeWeb Corporation |
Hsinchu |
N/A |
TW |
|
|
Assignee: |
Wistron NeWeb Corporation
(Hsinchu, TW)
|
Family
ID: |
54190017 |
Appl.
No.: |
14/613,370 |
Filed: |
February 4, 2015 |
Prior Publication Data
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Document
Identifier |
Publication Date |
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US 20150276929 A1 |
Oct 1, 2015 |
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Foreign Application Priority Data
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Apr 1, 2014 [TW] |
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103112128 A |
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
G01S
13/347 (20130101); G01S 13/58 (20130101); G01S
13/931 (20130101); G01S 13/52 (20130101); G01S
7/35 (20130101); G01S 7/356 (20210501); G01S
13/34 (20130101) |
Current International
Class: |
G01S
13/93 (20060101); G01S 13/58 (20060101); G01S
13/52 (20060101); G01S 13/34 (20060101); G01S
7/35 (20060101) |
Field of
Search: |
;342/112 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
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100478702 |
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Apr 2009 |
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CN |
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100590451 |
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Feb 2010 |
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CN |
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11344560 |
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Dec 1999 |
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JP |
|
Other References
Yan Wu et al., "Detection Performance Improvement of FMCW Radar
Using Frequency Shift", joint WIC/IEEESP Symposium on Information
Theory and Signal Processing in the Benelux, Brussels, Belgium, May
10, 2011, pp. 1-8. cited by applicant.
|
Primary Examiner: Bythrow; Peter M
Attorney, Agent or Firm: Hsu; Winston
Claims
What is claimed is:
1. A signal processing method for a frequency-modulated continuous
waveform (FMCW) radar system, comprising: receiving a plurality of
feedback signals from a plurality of targets, and performing analog
to digital conversion on the plurality of feedback signals, to
obtain a digital receiving signal corresponding to the plurality of
feedback signals; performing a window function transformation on
the digital receiving signal, to obtain a window transformation
signal corresponding to the digital receiving signal; performing
time-domain to frequency-domain conversion on the window
transformation signal, to obtain a spectrum signal of the window
transformation signal; performing two beat frequency detections on
the spectrum signal; and determining distances and speeds of the
plurality of targets in comparison to the FMCW radar system
according to results of the two beat frequency detections.
2. The signal processing method of claim 1, wherein the step of
performing the window function transformation on the digital
receiving signal is multiplying the digital receiving signal by an
window function.
3. The signal processing method of claim 2, wherein the window
function is selected from a rectangular window or a Hanning
window.
4. The signal processing method of claim 1, wherein the step of
performing the time-domain to frequency-domain conversion on the
window transformation signal is performing a discrete fast Fourier
transform, to convert the window transformation signal from a time
domain into a frequency domain and obtain the discrete spectrum
signal.
5. The signal processing method of claim 1, wherein the step of
performing the two beat frequency detections on the spectrum signal
comprises: performing a first round beat frequency detection on the
spectrum signal, to determine spectrum components greater than a
first threshold value within the spectrum signal, to obtain an
integer part of a plurality of normalized beat frequencies;
determining a fractional part of the plurality of normalized beat
frequencies according to the integer part of the plurality of
normalized beat frequencies; determining a complex gain of the
spectrum signal according to the integer part of the plurality of
normalized beat frequencies; cancelling a frequency component of
the spectrum signal according to the integer part of the plurality
of normalized beat frequencies, the fractional part of the
plurality of normalized beat frequencies, and the complex gain of
the spectrum signal, to obtain a double round spectrum signal,
wherein the double round spectrum signal corresponds to normalized
beat frequencies of targets not detected in the first round beat
frequency detection; and performing a second round beat frequency
detection on the double round spectrum signal, to determine
spectrum components greater than a second threshold value within
the spectrum signal.
6. A signal processing device for a frequency-modulated continuous
waveform (FMCW) radar system, comprising: an analog to digital
converter, for receiving a plurality of feedback signals from a
plurality of targets, and performing analog to digital conversion
on the plurality of feedback signals, to obtain a digital receiving
signal corresponding to the plurality of feedback signals; and a
digital signal processing module, for executing a digital signal
processing method, the digital signal processing method comprising:
performing a window function transformation on the digital
receiving signal, to obtain a window transformation signal
corresponding to the digital receiving signal; performing
time-domain to frequency-domain conversion on the window
transformation signal, to obtain a spectrum signal of the window
transformation signal; performing two beat frequency detections on
the spectrum signal; and determining distances and speeds of the
plurality of targets in comparison to the FMCW radar system
according to results of the two beat frequency detections.
7. The signal processing device of claim 6, wherein the step of
performing the window function transformation on the digital
receiving signal is multiplying the digital receiving signal by an
window function.
8. The signal processing device of claim 7, wherein the window
function is selected from a rectangular window, or a Hanning
window.
9. The signal processing device of claim 6, wherein the step of
performing the time-domain to frequency-domain conversion on the
window transformation signal is performing a discrete fast Fourier
transform, to convert the window transformation signal from a
time-domain into a frequency-domain and obtain the discrete
spectrum signal.
10. The signal processing device of claim 6, wherein the step of
performing two beat frequency detections on the spectrum signal
comprises: performing a first round beat frequency detection on the
spectrum signal, to determining spectrum components greater than a
first threshold value within the spectrum signal, to obtain an
integer part of a plurality of normalized beat frequencies;
determining a fractional part of the plurality of normalized beat
frequencies according to the integer part of the plurality of
normalized beat frequencies; determining a complex gain of the
spectrum signal according to the integer part of the plurality of
normalized beat frequencies; cancelling a frequency component of
the spectrum signal according to the integer part of the plurality
of normalized beat frequencies, the fractional part of the
plurality of normalized beat frequencies, and the complex gain of
the spectrum signal, to obtain a double round spectrum signal,
wherein the double round spectrum signal corresponds to normalized
beat frequencies of the targets not detected in the first round
beat frequency detection; and performing a second round beat
frequency detection on the double round spectrum signal, to
determining spectrum components greater than a second threshold
value within the spectrum signal.
11. The signal processing device of claim 6, wherein the digital
signal processing module comprises a memory and a processor, and
the memory stores a program code, for instructing the processor to
execute the signal processing method.
12. The signal processing device of claim 6, wherein the digital
signal processing module comprises: an window function unit, for
performing the window function transformation on the digital
receiving signal, to obtain the window transformation signal
corresponding to the digital receiving signal; a fast Fourier
transform unit, for performing the time-domain to frequency-domain
conversion on the window transformation signal, to obtain the
spectrum signal of the window transformation signal; a double round
spectrum detection unit, for performing two beat frequency
detections on the spectrum signal; and a range and velocity
estimation unit, for determining distances and speeds of the
plurality of targets in comparison to the FMCW radar system
according to results of the two beat frequency detections.
13. The signal processing device of claim 12, wherein the double
round spectrum detection unit comprises: a first round beat
frequency detection unit, for performing a first round beat
frequency detection on the spectrum signal, to determining spectrum
components greater than a first threshold value within the spectrum
signal, to obtain an integer part of a plurality of normalized beat
frequencies; a spectrum peak location estimation unit, for
determining a fractional part of the plurality of normalized beat
frequencies according to the integer part of the plurality of
normalized beat frequencies; a complex gain estimation unit, for
determining a complex gain of the spectrum signal according to the
integer part of the plurality of normalized beat frequencies; a
spectrum component cancellation unit, for cancelling a frequency
component of the spectrum signal according to the integer part of
the plurality of normalized beat frequencies, the fractional part
of the plurality of normalized beat frequencies, and the complex
gain of the spectrum signal, to obtain a double round spectrum
signal, wherein the double round spectrum signal corresponds to
normalized beat frequencies of the targets not detected in the
first round beat frequency detection; and a second round beat
frequency detection, for performing a second round beat frequency
detection on the double round spectrum signal, to determining
spectrum components greater than a second threshold value within
the spectrum signal.
Description
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a signal processing method and a
signal processing device for a frequency-modulated continuous
waveform (FMCW) radar system, and more particularly, to a signal
processing method and a signal processing device capable of
enhancing tracing stability of the FMCW radar system and reducing
missing rate of the FMCW radar system.
2. Description of the Prior Art
According to the statistics, most of traffic accidents are related
to drivers' distraction. If a driver is alerted at 0.5 seconds
before being likely to have a collision, it can avoid at least 60%
of rear-end collisions, 30% of head-on collisions and 50% of road
ramp related traffic accidents. If alerted before one second, it
can avoid 90% of traffic accidents. The statistics shows traffic
accidents can be effectively reduced if the drives have enough
reaction time. Vehicle alarm systems, e.g., a blind spot detection
(BSD) system, a forward/rear collision warning system, are smart
vehicle equipment developed for such needs.
Common vehicle alarm systems utilize frequency-modulated continuous
waveform (FMCW) radar technique to achieve early warning. More
specifically, the vehicle alarm system uses an image
self-recognition method of machine vision to detect obstacles in
specific areas on left/right/front sides of a vehicle, so as to
send out an alarm before collision happens. Nevertheless, under a
situation that there are two targets within a sensing area of the
FMCW radar system, if a velocity difference or a distance
difference of these two targets is so small that these two targets
may not be distinguished, a miss of the vehicle alarm system may
happen, i.e., the vehicle alarm system fails to send out an alarm
when the vehicle alarm system should alarm, which may indirectly
cause traffic accidents.
In such a situation, how to enhance an accuracy of the FMCW system
and reduce a missing rate of the FMCW system, so as to enhance
traffic safety, is a significant objective in the field.
SUMMARY OF THE INVENTION
It is therefore a primary objective of the present invention to
provide a signal processing method and a signal processing device
for frequency-modulated continuous waveform radar system, to
improve disadvantages of the prior art.
An embodiment of the present invention discloses a signal
processing method for a frequency-modulated continuous waveform
(FMCW) radar system, comprising receiving a plurality of feedback
signals from a plurality of targets, and performing analog to
digital conversion on the plurality of feedback signals, to obtain
a digital receiving signal corresponding to the plurality of
feedback signals; performing a window function transformation on
the digital receiving signal, to obtain a window transformation
signal corresponding to the digital receiving signal; performing
time-domain to frequency-domain conversion on the window
transformation signal, to obtain a spectrum signal of the window
transformation signal; performing two beat frequency detections on
the spectrum signal; and determining distances and speeds of the
plurality of targets in comparison to the FMCW radar system
according to results of the two beat frequency detections.
An embodiment of the present invention further discloses a signal
processing device for a frequency-modulated continuous waveform
(FMCW) radar system, comprising an analog to digital converter, for
receiving a plurality of feedback signals from a plurality of
targets, and performing analog to digital conversion on the
plurality of feedback signals, to obtain a digital receiving signal
corresponding to the plurality of feedback signals; and a digital
signal processing module, for executing a digital signal processing
method, the digital signal processing method comprising performing
a window function transformation on the digital receiving signal,
to obtain a window transformation signal corresponding to the
digital receiving signal; performing time-domain to
frequency-domain conversion on the window transformation signal, to
obtain a spectrum signal of the window transformation signal;
performing two beat frequency detections on the spectrum signal;
and determining distances and speeds of the plurality of targets in
comparison to the FMCW radar system according to results of the two
beat frequency detections.
These and other objectives of the present invention will no doubt
become obvious to those of ordinary skill in the art after reading
the following detailed description of the preferred embodiment that
is illustrated in the various figures and drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a schematic diagram of a frequency-modulated continuous
waveform radar system according to an embodiment of the present
invention.
FIG. 2 is a schematic diagram of the frequency-modulated continuous
waveform radar system in FIG. 1 sensing two targets.
FIG. 3 is a schematic diagram of a digital signal processing module
according to an embodiment of the present invention.
FIG. 4 is a schematic diagram of detail structures of a double
round spectrum detection unit in FIG. 3.
FIG. 5 is a schematic diagram of a digital signal processing
process according to an embodiment of the present invention.
FIG. 6 is a schematic diagram of a double round spectrum detection
process according to an embodiment of the present invention.
FIG. 7, 8 are schematic diagram of spectrums of embodiments of the
present invention.
DETAILED DESCRIPTION
Please refer to FIG. 1, which is a schematic diagram of a
frequency-modulated continuous waveform (FMCW) radar system 10
according to an embodiment of the present invention. The FMCW radar
system 10 is installed on a vehicle such as a car, a bus, a truck,
etc., for detecting whether an obstacle, such as another vehicle or
a person, is within a specific range, and sending out an alarm
signal accordingly, to avoid drivers causing traffic accidents
because of carelessness, blind spots, etc. The FMCW radar system 10
is functionally divided into a transmission portion 12 and a
reception portion 14. The transmission portion 12 comprises a
transmission antenna 120, a local oscillator 122 and a sweep
controller 124. The reception portion 14 comprises a reception
antenna 140, a frequency mixing and low pass filtering module 142,
an analog to digital converter 144 and a digital signal processing
module 146. Sensing operations of the FMCW radar system 10 can be
briefly described as follows. The sweep controller 124 controls the
local oscillator 122 to generate FMCW signals or other extensions
of FMCW signals, and emits the FMCW signals outward through the
transmission antenna 120. Correspondingly, the reception antenna
140 receives signals reflected from targets, the frequency mixing
and low pass filtering module 142 performs frequency mixing on the
reflected signals with the sinusoidal signal generated by the local
oscillator 122 and performs low pass filtering, to obtain beat
frequency signals between these two. The analog to digital
converter 144 samples the beat frequency signals and converts the
beat frequency signals into digital signals. The digital signal
processing module 146 computes and obtains information of the
targets such as ranges, moving speeds, etc., in relation to the
FMCW radar system 10.
In order to compute information of the targets such as ranges,
moving speeds, etc., the digital signal processing module 146 needs
to convert the digital beat frequency signals from time domain into
frequency domain. A common method is using fast Fourier transform
(FFT), but not limited thereto. Nevertheless, in order to reduce
spectrum leakage, before performing fast Fourier transform, the
digital signal processing module 146 may multiply the sampled beat
frequency signals by an window function in time domain, to avoid
mutual interference of the target reflected signals, which causes a
reduction of signal-to-noise ratio and affects performance of the
FMCW radar system 10. After the window function and fast Fourier
transformation, the digital signal processing module 146 utilizes a
fixed or a dynamic threshold value to detect the beat frequencies
of the targets, then utilizing the beat frequencies of two or
multiple chirp time according to different modulated patterns, or a
beat frequency and its phase information, to obtain the information
of the targets such as the ranges, the moving speeds, etc.
As can be seen, by using the window function, the fast Fourier
transformation and the beat frequency detection, the digital signal
processing module 146 may obtain the information of the targets
such as the ranges, the moving speeds, etc. Nevertheless, the
digital signal processing module 146 performs spectrum analysis in
a limited time, and the capability of distinguishing objects
thereof would be limited by a bandwidth of beat frequency f.sub.b
in frequency domain. For example, as shown in FIG. 2, if distances
of targets T1, T2 in relation to the reception antenna 140 are
R.sub.1, R.sub.2, respectively, and relative speeds are v.sub.r,1,
v.sub.r,2, respectively. The condition that the targets T1, T2 can
be distinguished correctly by the digital signal processing module
146, i.e., of the beat frequency corresponding to the targets T1,
T2 in frequency domain being correctly resolved is:
|R.sub.1-R.sub.2|.gtoreq.2D.DELTA.R or
|v.sub.r,1-v.sub.r,2|.gtoreq.2D.DELTA.V (eq. 1); where
.DELTA..times..times..times..times. ##EQU00001## is a range
resolution of the FMCW radar system 10 determined by the bandwidth
B of the sweep controller 124,
.DELTA..times..times..times..times..times. ##EQU00002## is a
velocity resolution of the FMCW radar system 10 determined by an
initial frequency f.sub.0 and a modulation time T.sub.m of the
sweep controller 124, and D.gtoreq.1, which is an affection caused
by a main-lobe attenuation of the window function.
As can be seen from eq. 1, when the velocity difference of the
targets T1, T2 is smaller than 2D.DELTA.V and the range difference
is smaller than 2D.DELTA.R, the targets T1, T2 are not able to be
distinguished by the FMCW radar system 10, which may affect an
accuracy of tracing targets and cause a miss, i.e., an alarm fails
to be sent out when it should be. Traffic accidents may even be
indirectly caused.
In order to enhance the accuracy of the FMCW radar system 10, the
present invention further modifies the operations of the digital
signal processing module 146, in which a double round spectrum
detection process is utilized to detect beat frequencies in
spectrum which are close to each other, so as to improve the
accuracy of tracing targets and reduce the missing rate of radar.
In detail, please refer to FIG. 3, which is a schematic diagram of
a digital signal processing module 30 according to an embodiment of
the present invention. The digital signal processing module 30 is
applied in the FMCW radar system 10, and may replace the digital
signal processing module 146 in FIG. 1. The digital signal
processing module 30 comprises an window function unit 300, a fast
Fourier transform unit 302, a double round spectrum detection unit
304 and a range and velocity estimation unit 306. Moreover, the
double round spectrum detection unit 304 may detect beat
frequencies which are closed to each other in frequency domain.
That is, the double round spectrum detection unit 304 performs a
first round beat frequency detection and regards the frequency
components detected from the first round detection as interference
to other smaller targets. Through a spectrum peak location
estimation, a more accurate spectrum location information is
obtained. After spectrum elimination, the double round spectrum
detection unit 304 performs a second round target detection, to
acquire a beat frequency information of another target which is
originally covered. In such a situation, after the double round
spectrum detection, the condition of targets being distinguishable
is improved as: |R.sub.1-R.sub.2|.gtoreq.2D.DELTA.R.alpha. or
|v.sub.r,1-v.sub.r,2|.gtoreq.2D.DELTA.V.alpha.,
0.ltoreq..alpha..ltoreq.1 (eq. 4); where .alpha. is an improving
factor, which can be achieved as 0.6 at least. In other words,
targets not distinguished by the digital signal processing module
146 are distinguished and detected by the digital signal processing
module 30 because of the use of the double round spectrum detection
unit 304.
For clearly explaining the operational principles of the digital
signal processing module 30, a received signal model of the FMCW
radar system 10 is analyzed first, and a signal processing method
of the digital signal processing module 30 is then described.
First of all, suppose at time t, there are N.sub.t targets
(N.sub.t>=1) within a sensing area or a surrounding area of the
FMCW radar system 10. In the k.sup.th chirp time, without
considering noise, a received signal x(t) outputted by the
frequency mixing and low pass filtering module 142 to the analog to
digital converter 144 can be represented as:
.function..times..times..function..times..times..times..times..pi..times.-
.times..times..times..ltoreq.<.times. ##EQU00003## where A.sub.i
represents a complex gain of the i.sup.th target reflected signal
after merging phase information, f.sub.b,i is a beat frequency of
the target reflected signal, and T.sub.m represents a modulation
time of the FMCW signal. Suppose a sampling frequency of the analog
to digital converter 144 is F.sub.s, i.e., sampling time is
T.sub.s, a digital receiving signal x[n] after sampling is:
.function..times..times..function..times..times..times..pi..times..times.-
.times..times..times. ##EQU00004## In order to fit requirements of
FFT to be time efficient, the modulation time T.sub.m is set to be
T.sub.m=NT.sub.s, where N is a power of 2. A frequency resolution
.DELTA.f of FFT is .DELTA.f=F.sub.s/N. As mentioned in the above,
when the discrete beat frequency
##EQU00005## is not an integer multiple of the frequency resolution
.DELTA.f, spectrum leakage occurs, which causes mutual interference
among the target reflected signals and causes reduction of
signal-to-noise ratio. Therefore, the window function unit 300 of
the digital signal processing module 30 is utilized for multiplying
the digital receiving signal x[n] by an window function w[n] in
time domain, where the window function w[n] may be a rectangular
window, a Hanning window, or other types of window functions.
Nevertheless, the window function w[n] widens the spectrum of the
digital receiving signal x[n] in D times, and reduces the range and
velocity resolution. Specifically, a window transformation signal
r[n], which is the digital receiving signal x[n] converted through
the window function w[n], is:
.function..function..function..times..function..times..function..times..t-
imes..times..pi..times..times..times..times..times..times..times..times.
##EQU00006##
Assume the sampling point N in eq. 7 is infinite for facilitating
the analysis. Mathematically, after performing discrete time
Fourier transform (DTFT), the window transformation signal r[n]
outputted by the window function unit 300 is converted as a
spectrum signal, which is:
.function..times..pi..times..times..times..function..times..pi..times..ti-
mes..function..times..pi..times..times..times..times..pi..times..times..ti-
mes..function..times..pi..times..times..times..delta..function..times..pi.-
.function..times..times..pi..times..times..times..function..times..pi..fun-
ction..times. ##EQU00007## where (*) is a convolution operator, and
.delta.(f) is an impulse function in frequency domain. Results of a
finite length FFT may be regarded as results of performing sampling
on the continuous spectrum obtained by DTFT, which is:
.function..times..function..times..pi..times..times..times..times..times.-
.times..times..times..function..times..pi..function..times..times..times..-
times..times..function..times..pi..times..times. ##EQU00008## where
R[k] and W[k] respectively represent the discrete spectrum signals
of the digital receiving signal x[n] and the window function w[n],
and
##EQU00009## is a normalized beat frequency.
As can be seen from eq. 9, the discrete spectrum signal R[k], which
is obtained by performing FFT on the received signal x(t) under
multiple targets environment, is results of performing sampling in
frequency domain on the summation of different shifted version of
the window function w[n] in frequency domain. As can be seen from
the signal model, when two targets are too close to each other, the
two targets might not be distinguishable. However, since the
spectrum of the window function w[n] is known, if the normalized
beat frequency q.sub.b,i and the complex gain A.sub.i are correctly
obtained, part of spectrum components can be cancelled, so as to
eliminate affection of the detected target beat frequencies on
other target beat frequencies, and acquire target beat frequencies
which are originally covered.
Please refer to FIG. 4, which is a schematic diagram of detail
structures of the double round spectrum detection unit 304. The
double round spectrum detection unit 304 comprises a first round
beat frequency detection unit 400, a spectrum peak location
estimation unit 402, a complex gain estimation unit 404, a spectrum
component cancellation unit 406 and a second round beat frequency
detection 408. The first round beat frequency detection unit 400 is
utilized for obtaining the beat frequencies of the targets, and
employs a fixed or a floating threshold value, e.g., a constant
false alert rate (CFAR) detector to perform detection on the
discrete spectrum signal R[k], to acquire spectrum components
within the discrete spectrum signal R[k] which are greater than the
threshold values and find the spectrum peak locations. However,
limited by the frequency resolution, the first round beat frequency
detection unit 400 only acquires integer parts k.sub.D,m of the
beat frequencies, which is k.sub.D,m=Round(q.sub.D,m),
0.ltoreq.m.ltoreq.N.sub.D (eq. 10) where Round(.) represents an
operation of outputting the closest integer. Each detected beat
frequency q.sub.D,m corresponds to a beat frequency q.sub.b,i of a
real target. Limited by the resolution, only m=N.sub.D,1 targets
are detectable.
Next, the spectrum peak location estimation unit 402 is utilized
for a finer frequency estimation. First, the frequency detected in
eq. 10 can be rewritten as: q.sub.D,m=k.sub.D,m+p.sub.m
0.ltoreq.m<N.sub.D,1 (eq. 11); where p.sub.m is a fractional
part of the m.sup.th detected frequency. As known in the art, this
fractional part may be estimated by
.function..function..function..function..function..function..times..ltore-
q.<.times..times. ##EQU00010## where |.| is an operation of
taking amplitude of complex signal, and P is an adjusting factor
corresponding to different window functions. After obtaining the
frequency integer part k.sub.D,m from the first round target
detection, the complex gain estimation unit 404 may perform the
following operation, to obtain estimate values of the complex
gains:
'.function..function..times..pi..times..ltoreq.<.times.
##EQU00011##
The spectrum component cancellation unit 406 performs frequency
component cancellation according to the estimated frequencies and
the estimated complex gains, to obtain a double round spectrum
signal R.sub.2[k] as:
.function..times..function..times.'.times..function..times..pi..times..lt-
oreq.<.times..times.'.times..function..times..pi..times..ltoreq.<.ti-
mes. ##EQU00012##
As can be seen from eq. 14, by cancelling the frequency components
within the discrete spectrum signal R[k], the double round spectrum
signal R.sub.2[k] only contains targets which are not detected by
the first round beat frequency detection unit 400. At this time,
the second round beat frequency detection 408 performs the second
target detection according to the eliminated frequency amplitude to
obtain information of the rest of the targets. Thereby, the
targets, which are not distinguishable in eq. 1, may be
detected.
The operations of the digital signal processing module 30 described
in the above can be summarized into a digital signal processing
process 50, as shown in FIG. 5. The digital signal processing
process 50 comprises following steps:
Step 500: Start; after the analog to digital converter 144 receives
a plurality of feedback signals from a plurality of targets, and
performs analog to digital conversion on the plurality of feedback
signals to determine the digital receiving signal x[n], the digital
signal processing process 50 is started.
Step 502: The window function unit 300 multiplies the digital
receiving signal x[n] by the window function w[n], to obtain a
window transformation signal r[n].
Step 504: The fast Fourier transform unit 302 performs time-domain
to frequency-domain conversion on the window transformation signal
r[n], to obtain the discrete spectrum signal R[k].
Step 506: The double round spectrum detection unit 304 performs two
beat frequency detections on the discrete spectrum signal R[k].
Step 508: The range and velocity estimation unit 306 determines
distances and relative speeds of the plurality of targets according
to output results generated by the double round spectrum detection
unit 304.
Step 510: End.
Moreover, the operations of the double round spectrum detection
unit 304 can be summarized into a double round spectrum detection
process 60, as shown in FIG. 6. The double round spectrum detection
process 60 comprises following steps:
Step 600: Start.
Step 602: The first round beat frequency detection unit 400
determines spectrum components within the discrete spectrum signal
R[k] which are greater than a first threshold value, to obtain
integer parts of a plurality of normalized beat frequencies.
Step 604: The spectrum peak location estimation unit 402 determines
fractional parts of the plurality of normalized beat frequencies
according to the determination results generated by the first round
beat frequency detection unit 400.
Step 606: The complex gain estimation unit 404 determines complex
gains of the discrete spectrum signal R[k] according to the
determination results generated by the first round beat frequency
detection unit 400.
Step 608: The spectrum component cancellation unit 406 cancels
frequency components of the spectrum signal according to the
determination results generated by the first round beat frequency
detection unit 400, the determination results generated by the
spectrum peak location estimation unit 402 and the determination
results generated by the complex gain estimation unit 404, to
obtain the double round spectrum signal R.sub.2[k], wherein the
double round spectrum signal R.sub.2[k] corresponds to normalized
beat frequencies of targets not detected by the first round beat
frequency detection unit 400.
Step 610: The second round beat frequency detection 408 determines
spectrum components within the double round spectrum signal
R.sub.2[k] which are greater than another threshold value.
Step 612: End.
Detail operations of the digital signal processing process 50 and
the double round spectrum detection process 60 can be referred to
the relative paragraphs of the embodiments stated above, and are
not narrated herein for brevity. Moreover, a combination of the
operations of the analog to digital converter 144 and the
operations of the digital signal processing module 30 (i.e., the
digital signal processing process 50) maybe regarded as a signal
processing method applying for the FMCW radar system 10.
Correspondingly, a combination of the analog to digital converter
144 and the digital signal processing module 30 may be regarded as
a signal processing device applying for the FMCW radar system
10.
As can be seen from the above, after the double round beat
frequency detection, the digital signal processing module 30 is
able to detect targets which are not distinguishable in eq. 1,
effectively enhances the tracing accuracy of the FMCW radar system
10, and reduces the missing rate of the radar system, so as to
enhance traffic safety. Notably, the digital signal processing
module 30 is an embodiment of the present invention, which employs
blocks representing programming code or operation principles of
different processes. In fact, the digital signal processing module
30 may be implemented by a processor and a memory. The memory
stores programming codes corresponding to the digital signal
processing process 50 and the double round spectrum detection
process 60, to instruct the processor to perform the related
operations. The processor applied for the digital signal processing
module 30 may be a microprocessor or application-specific
integrated circuits (ASIC). The memory applied for the digital
signal processing module 30 may be any information storage device
such as read-only memory (ROM), random-access memory (RAM),
CD-ROMs, magnetic tapes, floppy disks, optical data storage
devices, etc., and are not limited herein.
In addition, the aforementioned embodiments illustrate a double
round detection. In fact, those who skilled in the art may
adequately derive detection processes which comprise more than two
rounds, and are not limited herein. Moreover, the threshold values
used by the first round beat frequency detection unit 400 and the
second round beat frequency detection 408 may be different or the
same. The threshold values may also be constant values or variable
values, depending on the system requirements. Furthermore, the FMCW
radar system 10 may be applied on blind spot detection (BSD)
systems, forward/rear collision warning systems, but not limited
herein. All FMCW radar systems using machine vision to recognize
targets may adopt the detection method of the present
invention.
The improvement of the accuracy of the FMCW radar system 10
utilizing the digital signal processing module 30 or the digital
signal processing process 50 can be verified by experiments or
simulations. For example, in FIG. 2, suppose a bandwidth used by
the FMCW radar system 10 is 150 MHz, the chirp time is 10 ms, and
an initial frequency f.sub.0 of the FMCW sweep controller 124 is 24
GHz, the FMCW radar system 10 is disposed at an front end of the
vehicle, and the relative speeds v.sub.r,1, v.sub.r,2 of the
targets T1, T2 are 12.5 m/s, the distances of the targets T1, T2 in
relation to the reception antenna 140 are 18.4 meter and 20 meters.
In such a situation, if the FMCW radar system 10 does not use the
double round detection of the digital signal processing module 30
(i.e., using the digital signal processing module 146), according
to eq. 1, the range resolution and the velocity resolution are 1
meter and 0.625 m/s. In other words, a capability of distinguishing
targets is only 2 meters. Thus, three conditions might happen: (1)
a reflection energy of the target T1 is much larger than a
reflection energy of the target T2, only the target T1 is detected
by the radar, and the target T2 is missed; (2) a reflection energy
of the target T2 is much larger than a reflection energy of the
target T1, only the target T2 is detected by the radar, and the
target T1 is missed; (3) if the reflection energy of the targets
T1, T2 are comparable, no target is detected at the original
positions of the targets T1, T2, and a merging ghost target is
detected at an average position of the targets T1, T2, causing a
wrong alert.
In comparison, when the FMCW radar system 10 adopts the double
round detection mechanism of the digital signal processing module
30 of the present invention, according to the above parameters, the
digital beat frequencies are 38.4 and 40. Suppose that the complex
gain of the target T1 is 1 and the complex gain of the target T2 is
0.2, the spectrum obtained by FFT is shown as FIG. 7. In FIG. 7,
triangles represent the frequency sampling points, a curve Sp_T1
represents the FFT results of the target T1, a curve Sp_T2
represents the FFT results of the target T2, a curve SSp represents
a summation of the FFT results of the targets T1 and T2, TH1
represents a threshold value used in the first round beat frequency
detection unit 400, pk_d1 represents a spectrum component
corresponding to the target T1 in the first round beat frequency
detection, and pk_tr represents the actual spectrum component
corresponding to the target T1. Therefore, after the first round
beat frequency detection, only the target T1 is detected, and the
discrete beat frequency is 38, which is an integer part of the
actual beat frequency. Next, according to the operations of eq. 12,
eq. 13 and eq. 14 stated in the above, the frequency component of
the target T1 is eliminated, and the eliminated spectrum is shown
in FIG. 8. In FIG. 8, triangles represent the sampling points, a
curve Sp_T2 represents the FFT results of the target T2, TH2
represents a threshold value used in the second round beat
frequency detection unit 408, and pk_d2 represents a spectrum
component corresponding to the target T2 in the second round beat
frequency detection. Therefore, as can be seen from FIG. 8, the
eliminated spectrum, in which the spectrum components of the target
T1 are eliminated, matches the actual spectrum of the target T2.
The second round beat frequency detection is performed on the
eliminated spectrum, and the beat frequency information of the
target T2 may be obtained. Hence, after the double round beat
frequency detection, both the targets T1, T2 are detected
correctly, and there is no miss caused by too close distances or
velocities of targets and no wrong alert caused by ghost
targets.
As can be seen from the above, the double round beat frequency
detection process may improve the object distinguishing capability
of the FMCW radar system, and protect small targets from being
covered by large targets with close distance and velocity, so as to
enhance the tracing stability of the FMCW radar system, reduce the
missing rate of the FMCW radar system, and enhance the traffic
safety.
Those skilled in the art will readily observe that numerous
modifications and alterations of the device and method may be made
while retaining the teachings of the invention. Accordingly, the
above disclosure should be construed as limited only by the metes
and bounds of the appended claims.
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